[PATCH] D62786: [X86] X86DAGToDAGISel::matchBitExtract(): pattern a: truncation awareness

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: craig.topper, RKSimon, spatel.
lebedev.ri added a project: LLVM.

Finally tying up loose ends here.

The problem is quite simple:
If we have pattern `(x >> start) &  (1 << nbits) - 1`,
and then truncate the result, that truncation will be propagated upwards,
into the `and`. And that isn't currently handled.

I'm only fixing pattern `a` here,
the same fix will be needed for patterns `b`/`c` too.

I *think* this isn't missing any extra legality checks,
since we only look past truncations. Similary, i don't think
we can get any other truncation there other than i64->i32.


Repository:
  rL LLVM

https://reviews.llvm.org/D62786

Files:
  lib/Target/X86/X86ISelDAGToDAG.cpp
  test/CodeGen/X86/extract-bits.ll

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